Epigenetic Regulation of Hematopoietic Stem Cell Specification SUMMARY Leukemia is a multifaceted disease of disrupted cell function, aberrant gene expression and sustained survival. Some characteristics of leukemia cells are reminiscent of stem cell functions, such as the ability for self-renewal. How cancer cells obtain or re-acquire these characteristics remains unknown, though a role for chromatin remodeling is suggested by the presence of chromatin remodeling factors in translocation products. Similarly, much remains unknown regarding chromatin remodeling in hematopoietic stem cell (HSC) development. Here, we propose to uncover chromatin remodeling factors that regulate HSC specification using zebrafish as a model system. To this end, we will elucidate the role of the Polycomb family of chromatin remodelers in hematopoiesis and establish a hierarchy for Polycomb activity in relation to the Wnt and Notch pathways, both essential in hematopoietic specification and maintenance. We will also conduct a reverse genetic screen using a morpholino-based gene expression knockdown approach to reveal factors necessary for the establishment of HSCs and the HSC epigenetic code. As many of the pathways and regulators associated with leukemia also control hematopoiesis, defining the basic mechanisms of HSC specification and maintenance will illuminate critical factors in normal cell function that cancerous lesions exploit and thus be targeted in therapeutic approaches. PUBLIC HEALTH RELEVANCE: The studies outlined in this proposal will identify factors that alter hematopoietic stem cell development and, when misregulated, may contribute to a leukemic phenotype. Our work aims to identify novel leukemic markers and more accurately determine a diagnosis and prognosis for leukemia patients. Furthermore, knowledge of specific genetic defects may help in selecting a particular course of treatment and may be useful in developing new therapies.